[AC/Heater] Heated Rear Window - Auto On?

[Kpow99]

Yes 06 2.2 EX

[Bardley]

No, March '06 1.8 SE

[kryten]

If you drive a diesel then under certain conditions the HRW and mirrors will come on by themselves, this is not true of the petrol versions. Does anybody want the exact specs for when this system will self activate?

[dieseldriver]

voted yes
Sept 07 2.2d EX

[FWH]

Originally Posted by kryten

If you drive a diesel then under certain conditions the HRW and mirrors will come on by themselves, this is not true of the petrol versions. Does anybody want the exact specs for when this system will self activate?

Yes please.

[Sandozer]

OK, give us the gen...!

[trista]

Yes, UK 2.2. MY08

[kryten]

Ok heres how it works.

Rear defrost control.
1) Ignition must be switched on.
2) The rear def/heated mirror is switched on and off by the switch.

Timer function.
After activation by the user pressing the switch:
1) The control unit looks at the outside air temperature and if it is below 0°C keeps the rear defroster/mirrors on for 40 minutes or until the switch is pressed to turn it off.
2) If the outside temperature is above 0°C but below 30°C then the time the defroster is on is reduced to an amount of time between 40 and 20 minutes depending on the outside temperature. Above 30°C outside temperature the amount of time the unit is on is set to 20 minutes.
3) The timer function is cancelled with rear def/mirror switch operation.

Auto operation (Diesel only)
In addition to the functions listed above the Diesel has a hidden operation mode.

1) IGN must be ON, with engine rpm above 500 rpm and blower turned ON.
2) Outside temperature is below 10°C and engine coolant temperature is below 75°C.
3) If the previous 2 conditions are met then the rear defroster/heated mirrors are automatically turned on and follows the timer functionality as stated above.
4) If the outside temperature goes above 10°C or engine coolant temperature is above 75°C the rear defroster turns off, it then needs outside temperature to drop below -5°C or engine coolant temperature to drop below 50°C for the rear defroster/mirrors to turn back on again.
5) If the user operates the switch the Auto function is cancelled and will not restart until the ignition is switched off and then on again.

[FWH]

Thanks, you don´t happen to know why this is only on the diesel cars?

[kryten]

This auto function is in place so that the extra electrical load on the alternator makes the engine work slightly harder so speeding up warm up time and lowering emissions as well and as diesels take longer to warm up thats why only diesel engined models have this function

[FWH]

Great!

Any other "easter eggs" we should know about?

[Sandozer]

Originally Posted by kryten

This auto function is in place so that the extra electrical load on the alternator makes the engine work slightly harder so speeding up warm up time and lowering emissions as well and as diesels take longer to warm up thats why only diesel engined models have this function

Superb, Kryten... You the Man....

[dieseldriver]

Originally Posted by kryten

This auto function is in place so that the extra electrical load on the alternator makes the engine work slightly harder so speeding up warm up time and lowering emissions as well and as diesels take longer to warm up thats why only diesel engined models have this function

Thanks for this kryten, I always wondered why my heater was on and the light wasn't.....Good work...

[GHGH]

But why???

[TTDegs]

What a result!

Many thanks to everyone who contributed, and to Kryten for giving us the exact low down

[dylang652]

From Wiki:
The orange light on the dashboard switch does not illuminate when this happens.

Originally Posted by cjthompson321

So how do you know it's working? Do you have to wait for a frosty day and wait to see what happens?

If the rear screen is frozen when i get in i press the button straight away.

I'm going to withdraw my vote.

Please removed me from the stats. July 07 2.2 Type S GT

Ooh Err! I do the same - I will try to restrain myself next time there is a frost - take mine off for now as well please!

[mike20]

Originally Posted by kryten
This auto function is in place so that the extra electrical load on the alternator makes the engine work slightly harder so speeding up warm up time and lowering emissions as well and as diesels take longer to warm up thats why only diesel engined models have this function

I'm sorry I'm not sure that makes sense to me. Thats like saying turn all your lights and air con on and it'll lower emissions because the engine's working harder.
I do realise that the emissions are directly affected by the rate that the engine warms up but deliberately forcing the engine to work harder to achieve it seems a negative way of doing it.

[Honda100]

Yes to a 2.2 2006 ES and a 2.2 2007 EX

[TTDegs]

Anyone who wants to change their vote can click the 'withdraw vote' just underneath the results at the top of each page of this thread

But it is all looking pretty conclusive!

If you have a 2.2, it should auto defrost, and if you have a 1.8 or 2.0 engine, then you need to press the button yourself



And for clarity - auto defrost means that the film of ice on the rear window / wing mirrors will clear without you having to press the button.
The LED does not light up when auto defrost is doing it's thing

[Foggy69]

Originally Posted by TTDegs

If you have a 2.2, it should auto defrost, and if you have a 1.8 or 2.0 engine, then you need to press the button yourself

Blimey, you have to pay a £1300 premium to have a car with an auto defrost rear screen. That's a bit steep, even for Honda.
Oh, I see, you get a noisy, smelly and dirty lump of metel under the bonnet as well